1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices. More particularly, the present invention relates to a photoresist purge control device of equipment for coating semiconductor wafers with photoresist.
2. Description of the Related Art
In general, the manufacturing of a semiconductor device includes fabricating, assembly and test processes. For example, the fabricating process may entail subjecting a silicon wafer repeatedly to individual diffusion, photolithography, etching and thin film-forming processes, to thereby form an electric circuit on the wafer. At this time, the fabricating process leaves the wafer in a semi-finished state. The semi-finished wafer is then subjected to the assembly process. In the end, the test process ensures that the electric circuit is operating perfectly.
In the photolithography process, an oxide is formed on the surface of the silicon wafer, to protect a polished surface of the wafer. Photoresist in a liquid state is dispensed onto the oxide, and then the wafer is rotated at a high speed to form a uniform film of the photoresist on the oxide. A mask is disposed over the wafer coated with the photoresist. Light is directed onto the photoresist through the mask and only the portion of the photoresist exposed to the light undergoes a reaction (with the light) that produces a virtual image on the photoresist. Then, the photoresist is developed, whereby the photoresist attains a pattern corresponding to the virtual image. Portions of thin films exposed by the photoresist pattern are selectively removed through an etching process using gas or chemicals to thereby form a corresponding pattern in the thin films. In such a photo-etching process, the quality of the photoresist layer is considerably important in producing the desired pattern in the underlying film(s). For instance, the accuracy of the critical dimension (CD) of the electric circuit depends, in part, upon the thickness of the photoresist deposited on the wafer.
A known device for depositing photoresist on a wafer includes storage bottles containing photoresist, a photoresist deposition pipe connected to the storage bottles and through which photoresist is dispensed onto a wafer, an exchange valve operable to selectively deliver photoresist from the storage bottles to the photoresist deposition pipe, and an auxiliary sensor connected between the exchange valve and the photoresist deposition pipe to sense the amount of photoresist remaining in the line. The auxiliary sensor allows for the prevention of unwanted bubbles from being produced in the photoresist film.
Furthermore, a device for uniformly applying photoresist onto a wafer is disclosed in U.S. Pat. No. 6,332,924 B1. In this device, the photoresist is dispensed through a nozzle onto the wafer, and the amount and pressure of the photoresist is kept constant to ensure that the photoresist is deposited uniformly on the wafer.
Photoresist spraying devices must also be capable of supplying several different types photoresist, because different lots of wafers often require photoresists having different properties. In this case, after first photoresist is dispensed from a first bottle through a supply line onto the wafers of one lot, the supply line is purged to remove any of the first type of photoresist remaining in the supply line. Then, the supply line is connected with another bottle that is filled with a second photoresist having a characteristic different from that of the first photoresist.
FIG. 1 schematically shows such a conventional photoresist supply device. The conventional photoresist supply device includes a plurality of photoresist bottles 10, 12 storing the same kind of photoresist. First and second supply pipes 14, 16 are respectively connected to upper parts of the photoresist bottles 10, 12. First and second sensors 18, 20 are installed in the first and second supply pipes 14, 16 for sensing when the first and second supply pipes 14, 16 are empty, respectively. An air valve 22 connected to the first and second supply pipes 14, 16, can be re-positioned so as to selectively supply the photoresist supplied through the first and second supply pipes 14, 16 in response to a given control signal. A third supply pipe 24 connected to the air valve 22 transfers the photoresist supplied through the pipe opened by the air valve 22 to a dispense pump 26. The dispense pump 26 pressurizes the photoresist supplied through the third supply pipe 24 to force the photoresist through a fourth supply pipe 28. The fourth supply pipe 28 is connected to a nozzle 30 for spraying the photoresist onto a wafer disposed within a coater bowl 32.
A main controller 34 controls the entire wafer coating process. In particular, the main controller is connected to the first and second empty sensors 18, 20 so as receive a photoresist empty state detection signal from the first and second empty sensors 18, 20 whenever one of the first and second supply pipes 14, 16 is empty, and controls the dispense pump 26 on the basis of the input from the first and second empty sensors 18, 20.
FIG. 2 is a flowchart of a conventional method of operating the spray device at the time photoresist bottles are to be changed upon the use of the same device to coat a new lot of wafers.
Referring now to FIGS. 1 and 2, a worker informs an engineer of a lot change once a deposition process of coating a first lot of wafers with photoresist is completed. Upon receiving this information, the engineer keys in a parameter value, representing a mode change of the equipment, to the main controller 34 (101).
At this time, the engineer who was informed of the lot change, checks whether the last wafer has been transferred out of the coater bowl 32 (102), and keys in a command to the main controller 34 to effect a transfer of the wafer if a wafer is still within the coater bowl 32. Once the last wafer has been transferred from the coater bowl 32, the engineer exchanges the first and second photoresist bottles 10, 12 with new bottles in which photoresist having a different characteristic, appropriate for the new lot of wafers, is stored (103).
Subsequently, the engineer keys in information, pertaining to the new photoresist, to the main controller 34 (104). The engineer also inputs a spray start command to the main controller 34. As a result, the main controller 34 drives the air valve 22 to place the first supply pipe 14 in communication with the third supply pipe 24 (105). Then, the main controller 34 drives the dispense pump 26 to spray the photoresist stored in the first photoresist bottle 10 (106) through the nozzle 30.
The engineer visually checks the first photoresist bottle 10 while the photoresist is being sprayed (107). Once ½ of the photoresist stored in the first photoresist bottle 10 has been consumed, the engineer initiates a purge operation. At this time, the engineer separates the first supply pipe 14 from the first photoresist bottle 10 (108).
Subsequently, the first empty sensor 18 senses an empty state, and applies information indicative of the empty state to the main controller 34 (109). At this time, the main controller 34 controls the air valve 22 and places the second supply pipe 16 in communication with the third supply pipe 24.
The engineer monitors the second photoresist bottle 12 by eye to determine when about ⅔ of the photoresist stored in the second photoresist bottle 12 is consumed (110). Consuming about ⅔ of the photoresist of the second photoresist bottle 12 is required to purge the previous photoresist from the second supply pipe 16, and subsequently from the downstream supply pipes 24, 28, so that only new photoresist is present in the line.
Next, the engineer separates the second supply pipe 16 from the second photoresist bottle 12 (111).
Then, the second empty sensor 20 senses an empty state, and issues a signal indicative of the empty state to the main controller 34. At this time, the main controller 34 stops the operation of the dispense pump 26 (112).
Next, the engineer keys in information to the controller 34 that the purge is completed, whereupon the current mode of operation is changed to a run progression mode. Also, the engineer informs a worker that the equipment is now programmed to operate in the run progression mode (113).
As was described above, an engineer has to observe photoresist bottles while the photoresist is being purged, and then separate a supply pipe from the photoresist bottles so that the main controller will judge that the supply pipe is empty. In this case, the engineer has to continuously observe the photoresist bottles for about 40 minutes to one hour. Therefore, a lot of manpower is dedicated to changing the photoresist bottle. If the engineer is not diligent in observing the purging of the photoresist and leaves his/her position, an excessive amount of the photoresist can be purged, i.e., the photoresist can be wasted.
Furthermore, an engineer uses his/her naked eye to sense the amount of the photoresist consumed during the conventional photoresist purge method. The engineer separates the supply pipe from the photoresist bottle when he/she judges that so much of the photoresist has been consumed. Accordingly, different amounts of photoresist may be consumed during purge methods carried out by different engineers.